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Aquaponics has been recognized as one of "ten technologies which could change our lives" by merit of its potential to revolutionize how we feed growing urban populations (Van Woensel et al. 2015). This soilless recirculating growing system has stimulated increasing academic research over the last few years and inspired interest in members of the public as documented by a high ratio of Google to Google Scholar search results in 2016 (Junge et al. 2017). For a long time, aquaponics has been primarily practiced as a backyard hobby. It is now increasingly used commercially due to strong consumer interest in organic, sustainable farming methods. A survey conducted by the CITYFOOD team at the University of Washington in July 2018 shows that the number of commercial aquaponic operations has rapidly increased over the last 6 years. This focused search for aquaponic operations identified 142 active for-profit aquaponic operations in North America. Based on online information, 94% of the farms have started their commercial-scale operation since 2012; only nine commercial aquaponic farms have been in operation for more than 6 years (Fig. 21.1).
Most of the surveyed aquaponic operations are located in rural areas and are often connected to existing farms to take advantage of low land prices, available
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Fig. 21.1 Existing aquaponic practitioners in North America, 142 commercial companies (red) and
17 research centers (blue), (CITYFOOD, July 2018)
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Fig. 21.2 Aquaponics across Europe: 50 research centers (blue) and 45 commercial companies (red). (EU Aquaponics Hub 2017)
infrastructure, and conducive building codes for agricultural structures. Regardless, a growing number of aquaponic operations are also located in cities. Due to their relatively small physical footprint and high productivity, aquaponic operations are well suited to practice in urban environments (Junge et al. 2017). Surveys undertaken under the auspices of the European Union (EU) Aquaponics Hub in 2017 identified 50 research centers and 45 commercial companies operating in the European Union (Fig. 21.2). These companies range in size from small to medium sized.
Space is a valuable commodity in cities. Urban farms have to be resourceful to find available sites such as vacant lots, existing rooftops, and underutilized warehouses that are affordable for an agricultural business (de Graaf 2012; De La Salle and Holland 2010). Urban aquaponic farms need to balance higher production costs with competitive marketing and distribution advantages that urban locations offer. The largest benefit for locating aquaponic operations in cities is a growing consumer market with an interest in fresh, high-quality and locally grown produce. When complying with local regulations for organic produce, urban farms can achieve premium prices for their aquaponically grown leafy greens, herbs, and tomatoes (Quagrainie et al. 2018). Unlike hydroponics, aquaponics also has the capacity to produce fish, further enhancing economic viability in an urban setting which often has diverse dietary needs (König et al. 2016). Urban aquaponic farms can also save some operational costs by reducing transportation distance to the consumer and reducing the need for crop storage (dos Santos 2016).
Urban environmental conditions can also be advantageous for aquaponic farms. Average temperatures in cities are higher than in rural surroundings (Stewart and Oke 2010). In colder regions particularly, farms can benefit from a warmer urban climate, which can help reduce heating demand and operational costs (Proksch 2017). Aquaponic farms that are integrated with the building systems of a host building can further utilize urban resources such as waste heat and COsub2/sub in exhaust air to benefit the growth of plants as an alternative to conventional COsub2/sub fertilization. Urban farms can also help mitigate the negative aspects of the urban heat island effect during the summer months. The additional vegetation, even if grown in greenhouses, helps to reduce the ambient temperature through increased evapotranspiration (Pearson et al. 2010). In aquaponics, the use of recirculating water infrastructure reduces overall water consumption for the production of both fish and lettuce and can, therefore, have a positive effect on the urban water cycle. Aquaponically-grown produce strives to close the nutrient cycle, thereby avoiding the production of agricultural run-off. Through smart resource management within major environmental systems, aquaponics helps to reduce excessive water consumption and eutrophication usually created by industrial agriculture.
Traditional agricultural techniques to extend the natural crop-growing season range from minimal environmental modifications, such as temporary hoop houses used on soil-based fields, to full environmental control in permanent facilities that allow for year-round production regardless of the local climate (Controlled Environment Agriculture 1973). The latter strategy is also known as controlled environment agriculture (CEA) and includes both greenhouses and indoor growing facilities. In addition to controlling the indoor climate, CEA also significantly reduces the risk of crop loss to natural calamities and the need for herbicides and pesticides (Benke and Tomkins 2017). Most aquaponic operations are conceived as CEA since they combine two complex growing systems (aquaculture and hydroponics), which both require controlled growing conditions to guarantee optimal productivity. Additionally, CEA enables year-round production to amortize high investment in aquaponic infrastructure and achieve premium crop prices at the market outside of the natural growing season. The performance of aquaponic farm enclosures is highly dependent on local climate and seasonal swings (Graamans et al. 2018).
As aquaponics is a relatively young discipline, most of the existing research is focused at the system level — for example, studies evaluating the technical integration of aquaculture with hydroponics in different configurations (Fang et al. 2017; Lastiri et al. 2018; Monsees et al. 2017). Whilst individual aquaponic system components and their interactions can still be further optimized for productivity, their performance within a controlled environment envelope has not been comprehensively addressed. Recent research in CEA has begun to assess hydroponic system performance in tandem with built environment performance, although there is only one study to date that models aquaponic system performance in a controlled envelope (Benis et al. 2017a; Körner et al. 2017; Molin and Martin 2018a; SanjuanDelmás et al. 2018).
The current expansion in interest in aquaponics led to the creation of several interdisciplinary aquaponics related research collaborations funded by the European Union (EU). The COST FA1305 project, which created the EU Aquaponics Hub (2014—2018) brought together aquaponics research and commercial producers to better understand the state of the art in aquaponics and to generate coordinated research and education efforts across the EU and around the world. Innovative Aquaponics for Professional Application (INAPRO) (2014—2017), a consortium of 17 international partners, aimed to advance current approaches to rural and urban aquaponics through the development of models and construction of prototypical greenhouses. The project CITYFOOD (2018—2021) within the Sustainable Urban Growth Initiative (SUGI), co-funded by the EU, Belmont Forum, and respective science foundations, investigates the integration of aquaponics in the urban context and its potential impact on global challenges of the food-water-energy nexus.